1. Field of the Invention
The invention relates in general to a vapor-driven piston-type engine and in particular to a vapor-driven piston-type engine that has a first fluid therein that receives heat from a heat source to vaporize the fluid and drive the piston engine and which includes therein a second closed fluid path in heat exchange relation with the first fluid path to increase the efficiency of the engine. In a still further embodiment, a plurality of the efficient vapor-driven piston-type engines are coupled one to another in different closed circuits whereby the fluid in the first closed circuit in a second or subsequent vapor-driven piston-type engine is heated by the first vapor-driven piston-type engine or by the fluid flowing through it.
2. Description of Related Art
A conventional vapor force piston device contains a vaporizable fluid, an evaporator for vaporizing the fluid, the vapor piston machine and a closed circuit in which the evaporator and the vapor piston machine are interposed for the transport of the fluid. Such a conventional vapor force device of this sort may be a steam power plant which uses water as a fluid. The evaporator is the steam generator and the vapor machine is a steam engine with pistons or a steam turbine driving a current generator.
However, water evaporates at 100.degree. C. under atmospheric pressure. In order to obtain a good efficiency, over-heated or super-heated steam at an even far higher temperature is required. This implies that for the evaporation in the steam generator, high quality and quantities of fuel are required. It further implies that the device cannot work on heat alone at a relatively low temperature even though it may be available in large amounts. Thus the supplied energy is relatively expensive.
In U.S. Pat. No. 3,218,802 and issued in the name of D. R. Sawle, a binary vapor power plant includes a sulfur cycle consisting of a heat source 10 which heats and vaporizes sulfur, a first stage sulfur heat engine 12 which converts the heat in the vapor into kinetic energy, and a heat exchanger 14 that receives the partially cooled sulfur and removes the remainder of the heat. The heat exchanger 14 heats the fluid in conduits 37, 41, and 43 to convey steam to a second stage heat engine 16. Similar systems have been employed at petrochemical plants that use ethylene-oxide reactors. The reactors are cooled by a high temperature, low pressure fluid (diphyl fluid). This fluid is sent to a heat exchanger to produce the super-heated steam. The steam was used in a steam turbine to compress ethylene gas. This system has very difficult problems to overcome since using sulfide, sulfur, phosphorus or even sodium is excluded because steel is hydrogen permeable and hydrogen with the above materials will give severe problems. This is a very high temperature device with saturated sulfur vapor at 682.degree. C. (1260.degree. F.).
In U.S. Pat. No. 4,070,862 issued to Doerner et al., a turbine in power station plants is provided with two different fluids such as water and H.sub.2. One of the problems is the leakage from one turbine site to the other. The invention is a choice of two liquids where the second liquid has a lower boiling point than the first liquid and returns the vapor condensate (linkage) to the boiler. The two liquids have low pressures compared to their temperatures at 800.degree. C. with 34 PSIA (234 kPa) and 450.degree. C. at 51 PSIA (352 kPa. Although there are no efficiency figures stated in this patent, the use of such high temperatures and low pressures must have a detrimental influence on the overall efficiency of the turbine.
In U.S. Pat. No. 4,700,543 to Krieger et al., a plurality of independent, closed Rankine cycle power plants, each of which has a vaporizer and is operated by serially applying a medium or low temperature source fluid to the vaporizers of the power plants for producing heat-depleted source fluid. The heat-depleted source fluid is applied to all of the preheaters in parallel. The power plants are shown to be turbines.
Thus, there is a significant need in the art for a vapor-driven piston-type engine that has high efficiency and which operates at relatively low temperatures.